Intercalation in the Chinese Calendar is after the eighth
month every 19 years and is called ren ba yue
(Double August). According to tradition, tragedy will
follow when the month is added at that time. [Gevisier]

Egyptian biochemist Rashad Khalifa (1935-1990) claimed that he discovered an intricate numerical pattern in the text of the Qur'an involving the number 19. Sura 74:30 reads: "Over it are nineteen."

In his August 1941 Afterward to Thomas Wolfe's book The Hills Beyond, NY, Wolfe's editor, Edward C. Aswell, remarks that Thomas Wolfe's second book, never published, was to have been titled K19. When Wolfe died, Aswell watched the train carrying his coffin go by. Train K19! [Haga]

The smallest prime that is equal to the product of its digits plus the sum of its digits: 19 = (1 * 9) + (1 + 9). [Losnak]

The Bahá'í calendar, established in the middle of the 19th century, is based on cycles of 19 years. Years are composed of 19 months of 19 days each. [Dybwad]

The first prime repfigit number. A repfigit (repetitive fibonacci-like digit) number is an n-digit integerN with the following property: if a Fibonacci-like sequence (in which each term in the sequence is the sum of the n previous terms) is formed, with the first n terms being the decimal digits of the number N, then N itself occurs as a term in the sequence. For example, if the digits of 19 start a Fibonacci-like sequence, then 19 appears as a term: 1, 9, 10, 19. These are also known as Keith numbers. [Beedassy]

The number of trailing 0's in 80!.

Amendment 19 to the United States Constitution gave women the right
to vote. [Filler]

19 European nations endorsed the first international ban on human cloning.

21 + 32 + 53 + 74 + 115 + 136 + 177 + 198 is prime.

Product 19 is a multi-vitamin and mineral cereal of toasted corn, oats, wheat, and rice.

The Rhind papyrus contained a problem to find x so that x plus one seventh of x will equal 19.

An idiot is someone with an intelligence quotient (IQ) less than or equal to 19. [Brenner]

In the game of Go, two players alternate in placing black and white stones on a large (19-by-19 line) ruled board, with the aim of surrounding territory.

Consider a chess endgame where a King plus Opposite-Colored Bishops (i.e., two Bishops each residing on opposite-colored squares) versus a King. The checkmate requires, at most, 19 moves (if the side with the bishops move first).

For k = 1, 2, 3, ... 19 at least one of the integers of the
form 6k + 1 or 6k - 1 is prime. [Crespi de Valldaura]

The smallest number of neutrons for which there is no stable isotope. [Hartley]

For decades, mathematicians the world over would open their doors to find the homeless Paul Erdős (1913-1996) announcing, "My brain is open!" It is rumored that for 19 hours a day, seven days a week, stimulated by coffee, and later by amphetamines, he worked on mathematics. One of his greatest achievements was the discovery of an elementary proof for the prime number theorem.

If we pretend = 60/19, then a radius of 57 gives a circumference of exactly 360. [Moody]

"The Sun" is numbered with 19 in Tarot cards.

The Metonic cycle, which involves the phase cycle of the Moon, is a period of about 19 Julian years. [Gevisier]

19 is the largest prime that can be expressed pandigitally in some baseb > 1 (19 = 201 in base 3). [Keith]

Earth's mass (5.9736 * 1024) and volume (1.083*1012) are both multiples of 19. Earth's volume is in fact a multiple of 192.

The first prime number presenting and meaning the same value within the "western" world and the "arabic" is the number 19. All other recognizable prime numbers are with the combination of a 1 and 9. [ThaCoDa]

The speed limit (in miles per hour) on the private roads of the Cambourne development near Cambridge, England. [Croll]

19 is the largest prime factor of 1444 - the smallest perfect square to end in three 4's. Note that 4 is the only non-zero digit that can repeat at the end of a perfect square, and the most consecutive 4's that can appear in such a place is three. [Litman]

19 divides the concatenation of the integers from 19 down to 1. [De Geest]

Professor Barabási and his team have found that the World Wide Web on average has 19 clicks of separation between webpages. [McAlee]

Article 19 of the Universal Declaration of Human Rights:
"Everyone has the right to the freedom of opinion and expression; this right includes freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers." [McAlee]

The second (and last) trip of the USS Absaroka across the Atlantic to European waters ended in New York in February 1919. On December 24, 1941, the Japanese submarine I-19 fired two torpedoes at that same ship, which was carrying a cargo of lumber, two miles off Pt. Fermin (San Pedro, California). The ship didn't sink but one sailor was killed by falling lumber. [Haga]

19 is the smallest prime of the form 3p + 2q, where p and q are twin primes. [Teofilatto]

Any number that is divisible by 19 will have this property: multiply the last digit by 2, then add that number to the remaining digits and the resulting number will be divisible by 19. E.g., 625632 is divisible by 19 because all of following results are divisible by 19:(62563 + 4 = 62567); (6256 + 14 = 6270); (627 + 0 = 627); (62 + 14 = 76); (7 + 12 = 19); (1 + 18 = 19). [Beedle]

19 is the only prime p less than 30 that does not divide 30, where p + 30 is composite. [Axoy]

19 is the only known number for which both (10^n-1)/9 and (10^n+1)/11 are primes.

Consider a square made of four rigid rods, hinged at the
ends. How many rods of the same type must be added to make
the square rigid in the plane? The answer is 19, which
makes a total of 23 rods (also prime). [McCranie]

Here is the mathematical code to determine if a number is
divisible by 19. Multiply everything in front of the last
digit by nine and subtract the last digit. If you get zero,
nineteen, or a multiple of nineteen, the number will be
divisible by 19. For example 57. Five times nine minus seven
equals 38. Since 19 divides evenly into 38, it divides
evenly into 57. Next example 114. Eleven times nine minus
four equals 95. Since 19 divides evenly into 95, it divides
evenly into 114. [Young]

19 is the smallest prime mentioned a prime number of times in the KJV Bible. [Opao]

The smallest multidigit number (coincidentally prime) that does not form a palindrome when added to its reversal. [Capelle]

The only two-digit prime n such that n!/reversal(n)+1 and
n!/reversal(n)-1 are both prime. [Patterson]

The first verse of the Qur'an (known as "Basmalah") consists of 19 Arabic letters. [Yuksel]

The following are primes: 19, 109, 1009, 10009. No other digit can replace the 9 and yield four primes. [This is the first entry listed as a "Prime Curio" in the book NUMBERS: Fun & Facts by J. Newton Friend; Charles Scribner's Sons, New York (1954); Library of Congress Catalog No. 54-8690, p. 45.]

Farideh Firoozbakht improved the Papadimitriou's conjecture
and proposed that every prime number p
greater than or equal to 19 can be written as p = 2q + 3r,
where q and r are odd primes. [Capelle]

An unistable polyhedron is stable on only one face. The simplest such polyhedron known requires 19 faces. Whether unistability is possible with fewer faces is an unsolved problem. [McCranie]

The first prime p such that p^2 is the reversal of a prime
(163). [Silva]

19 terms are required in the Gregory-Leibniz series, i.e.,
4(1 - 1/3 + 1/5 - 1/7 + 1/9 - ...), for the first
appearance of "3.1" in the decimal expansion of .

In chess positions with a king and pawn versus a king in
which pawn promotion can be forced, at most 19 moves are
required to promote the pawn (with best play by both
sides). [McCranie]

The smallest prime which is the sum of two semiprimes in two different ways. [Post]

19 is the only known prime of the form n^n - 8. The next prime in this form (if it exists) will have more than 34000 digits. [Firoozbakht]

The MathScience
Innovation Center in Richmond, Virginia, is governed by a 19-member board
consisting of a superintendent and school board member from
each consortium division and several at-large members.

19 is the smallest prime which is the sum of three discrete
composites (4 + 6 + 9). [Post]

Some positions (e.g., "superflip") on the original Rubik's Cube cannot be solved in 19 or less face turns.

Only known prime of the form p*prime(p)^p + 1, where p is
prime. [Firoozbakht]

Each individual batch of Maker's Mark Whisky is less than 19 barrels. [Leonard]

The number of emirps that can be shown on a 12-hour digital clock. [Fellows]

There are 19 visible diamond patterns on the surface of a
fully formed rhombic triacontahedron when structured using
a series of phi-ratio pyramids. An example being Roger von
Oech's Ball of Whacks. [Trace]

Thomas Jefferson argued that "Every constitution, then, and
every law, naturally expires at the end of NINETEEN years.
If it be enforced longer, it is an act of force, and not of
right." Thomas Jefferson to James Madison, 1789. [Yuksel]

Take the nine pairs (a,b) with a+b=19; take the sum a*b+19
for all these nine pairs; ALL the sums are primes. 19 is
the largest prime that will do this. [Bergot]

The only known prime p of form 4*q+7, where q and 4*p+7 are prime. [Loungrides]

Alpha Natural Resources (ANR) forecast coal use to grow more than competing fuels in 19 of the 26 years between 2010 and 2035.